Envelope feeding system and speed control for mail sorting machines

ABSTRACT

A speed control system for an envelope feeding mechanism used to feed envelopes to a pickoff device in a high speed mail sorting machine. The feeding mechanism includes a pair of toothed belts which convey the envelopes along an inclined surface. The side edges of the envelopes are received by a third toothed belt which is driven at an elevated position along a side panel. The belts are driven by a multiple speed electric motor controlled by electronic circuitry which automatically decrements or increments the motor speed if the envelopes are bunched together too tightly or too loosely. If the speed is decremented and the envelopes are still tightly bunched, the drive motor is stopped by a shutoff circuit which operates independently of the speed control circuit.

BACKGROUND OF THE INVENTION

This invention relates generally to high speed mail sorting equipmentand deals more particularly with an improved method and apparatus forautomatically controlling the speed at which envelopes are conveyed inthe magazine section of a mail sorting machine.

In order to efficiently sort the large volumes of mail that are sent andreceived each day by various businesses, institutions, governmentalunits and other entitles that handle large amounts of mail, varioustypes of mail sorting machines have been proposed. One type of highspeed mail sorter that has been successful is shown in by U.S. Pat. No.4,275,875 which issued to Roy Akers on June 30, 1981 and which is ownedby the assignee of the present application. In this type of machine, theenvelopes which are to be sorted are loaded on a magazine section of themachine with the envelopes situated side to side on edge. An envelopefeeding mechanism delivers the envelope supply to a pickoff station atwhich the envelopes are picked off one at a time from the envelopesupply by vacuum belts or another type of pickoff device. The envelopesare thereafter handled individually, and each envelope is conveyed pasta reading station at which its zip code or another code imprinted on theenvelope is read, either by a human operator or by a code readingdevice. Envelopes which have the same or a similar code are thereafterdirected into the same storage bins by the mail sorting equipment.

Although this type of machine has been favorably received and hasperformed well for the most part, it has not been wholly free ofproblems. One of the most difficult problems has been to assure that theenvelopes are repeatedly picked off one at a time from the envelopesupply in the magazine section of the machine. In order for the vacuumbelts to properly separate the individual envelopes from the envelopesupply, the feeding system must be able to accommodate different types,sizes and thicknesses of envelopes. For example, if relatively thinenvelopes are being sorted, there is a tendency for the envelopes tobunch tightly together and thus adhere to one another at the pickoffstation. This tightly bunched condition of the envelopes often resultsin double picking and other mispicking problems. Conversely, if theenvelopes are not held together tightly enough, as tends to occur whenthick envelopes are being handled, similar picking problems arise andthe through put of the machine also suffers.

Various types of envelope feeding mechanisms have been proposed fordelivery of the envelopes to the pickoff device, including chains,augers, belts, push blocks and other conveyor systems. In order topermit the feeding mechanism to accommodate different mail thicknesses,a speed control knob has been provided so that the operator can slow theenvelope feeder down when handling thin envelopes and speed it up whenhandling thicker mail. However, it is necessary for the human operatorof the machine to closely observe the feeding operation and to manuallyadjust the speed control knob according to the mail that is beinghandled at each particular time. Due to human error and inattention, itis common for the control knob to be ignored so that the feedingmechanism generally operates at a constant speed even when the mailthickness changes. Consequently, this type of arrangement does noteliminate the double picking problems and other inefficienciespreviously mentioned.

SUMMARY OF THE INVENTION

The present invention is directed to an improved envelope feedingmechanism and to an electronic control system which automaticallyassures that envelopes are fed to the pickoff station at the properrate. In accordance with the invention, the magazine section of a highspeed mail sorting machine is equipped with a pair of toothed belts forconveying the envelopes in the magazine. The belts travel along a floorpanel which is inclined from side to side to maintain the side edges ofthe envelopes against an inclined side panel. The bottom edges of theenvelopes are received in grooves formed between the teeth of theunderlying belts so that advancement of the belts advances the envelopesupply toward the pickoff station at the end of the magazine.

A third belt travels along the side panel and is elevated with respectto the other two belts. The elevated belt is also a toothed belt whichreceives the side edges of the envelopes in grooves formed between theteeth. This helps to convey the envelopes and maintains each envelope inan upright posture as it is fed toward the vacuum belts of the pickoffdevice. All three belts are driven at the same speed by a common drivesystem so that the envelopes do not beocme skewed or otherwisedisoriented as they approach the vacuum belts.

The speed at which the tooth belts are driven is controlledelectronically to assure a proper envelope feeding rate at all times. Aswitch which projects between the vacuum belts is depressed when mail ispresent at the pickoff station and is released when the pickoff stationis vacant. An electronic up/down counter decrements its count state whenthe switch is depressed and increments the count state when the switchis released. If the count state reaches the minimum or maximum,indicating that the envelopes are being fed too fast or too slow, thecounter provides an output signal which is used to slow down or speed upthe multiple speed electric motor which drives the toothed belts.Consequently, the envelope feeding device is automatically slowed downwhen the envelopes become too tightly bunched and is automaticallyspeeded up when the envelopes are too loose in the magazine section ofthe mail sorting machine.

It is an important feature of the invention that the counter decrementsthe count state faster than it is incremented. This results in arelatively fast decrease in the speed of the drive belts when theenvelopes are tightly bunched. It is less important to quickly speed upthe feeding mechanism when the envelopes are arranged too loosely, sothe speed is increased at less frequent intervals in this situation.

The electronic motor control system also includes a circuit whichoperates to deactivate the drive motor independently of the speedcontrol circuit. If the speed of the feeding mechanism is decrementedand the switch remains depressed for an additional time interval,indicating that the envelopes are still tightly bunched at the pickoffstation, the drive motor is deactivated to allow the envelope picker toeliminate the tightly bunched condition before additional envelopes arefed to the pickoff station. Because the motor shut off system isindependent of the speed control system, the speed setting continues todecrease even while the motor is deactivated. Thus, if the drive motoris inactive for a relatively long time, it comes back on at a slow speedbecause the envelopes are tightly bunched and a slow speed is desirablein this situation. Conversely, the motor comes back on at a relativelyhigh speed if it has been deactivated for only a short time because, inthis situation, the envelopes are not bunched as tightly and there is noneed for a slow motor speed.

DESCRIPTION OF THE DRAWINGS

In the accompanying drawings which form a part of the specification andare to be read in conjunction therewith and in which like referencenumerals are used to indicate like parts in the various views:

FIG. 1 is a top plan view of a mail sorting machine equipped with anenvelope feeding mechanism and control system constructed according to apreferred embodiment of the present invention, with the break linesindicating continuous length of the storage section of the machine;

FIG. 2 is a fragmentary plan view on an enlarged scale showing themagazine section and pickoff station of the mail sorting machine, withportions broken away for purposes of illustration;

FIG. 3 is a fragmentary sectional view taken generally along line 3--3of FIG. 2 in the direction of the arrows;

FIG. 4 is a fragmentary sectional view taken generally along line 4--4of FIG. 2 in the direction of the arrows;

FIG. 5 is a fragmentary sectional view taken generally along line 5--5of FIG. 4 in the direction of the arrows;

FIG. 6 is a fragmentary sectional view on an enlarged scale takengenerally along line 6--6 of FIG. 4 in the direction of the arrows; and

FIGS. 7 and 8 together provide a schematic diagram of the motor controlcircuitry which controls the drive motor of the envelope feedingmechanism.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings in more detail and initially to FIG. 1, ahigh speed mail sorting machine is generally designated by referencenumeral 10. The mail sorting machine 10 is of the same general type asthat disclosed in U.S. Pat. No. 4,275,875, issued to Roy Akers on June30, 1981, which application is incorporated herein by reference.

The main components of the mail sorting machine 10 are a magazinesection 12 which receives the envelopes that are to be sorted, a pickoffstation 14 at which the individual envelopes are separated one at a timefrom the supply of envelopes loaded on the magazine section 12, a readstation 16 at which the zip code or other sorting code imprinted on eachenvelope is read, and a storage section 18 which receives and holds thesorted envelopes. The individual envelopes are separated from theenvelope supply at the pickoff station 14 and are then delivered one ata time on edge past the read station 16 through a guide way 20 whichterminates at the input end of the storage section 18. In the storagesection of the machine, a plurality of sets of diverter gates 22selectively deflect the sorted envelopes into storage areas 24 locatedon opposite sides of the storage section 18. The storage areas 24 caneach be equipped with a plurality of separate storage bins (not shown),or the envelopes can be held in separate stacks by hinged plates 26 orother stacking devices. Guide plates 28 are located adjacent to each setof deflector gates 22.

The mail sorting machine 10 can be provided with a code reading device(not shown) located at the read station 16 beneath a cover panel 30. Thecode reading device can be an optical code reader or any other suitabletype of device capable of reading the codes that are imprinted on theenvelopes. Alternatively, a human operator can read the codes on theenvelopes and manually enter the codes on a key board or the like. Inany event, one of the deflector gates 22 is operated by electroniccircuitry in order to deflect the envelope into the proper bin or otherstorage area which corresponds to the code imprinted on the envelope.

The present invention provides an improved envelope feeding mechanismfor handling the envelopes in the magazine section 12, along with acontrol system for controlling the operation and speed of the feedingmechanism. With particular reference to FIGS. 2, 4 and 5, the magazinesection 12 of the machine has a frame 32 on which a vertical end panel34 is mounted at the input or upstream end of the magazine (the lowerend as viewed in FIG. 2). An inclined conveyor surface is provided by afloor panel 36 which extends the entire length of the magazine 12between the input end and the opposite or downstream end locatedadjacent the pickoff station 14.

As best shown in FIG. 4, panel 36 inclines downwardly from left to rightat an angle of approximately 5° from horizontal Extending upwardly fromthe lower or right side of the floor panel 36 is a side panel 38 whichlikewise extends the entire length of the magazine 12. The side panel 38is perpendicular to the floor panel 36 and is thus offset from verticalby about 5°. As shown in FIG. 4, the floor panel 36 provides a surfacewhich receives the long lower edges of envelopes E which are depositedin the magazine, while the side edges of the envelopes engage the sidepanel 38. The incline of the floor panel 36 assures that the side edgesof the envelopes E will remain against the side panel 38.

The inclined floor panel 36 is provided with a pair of parallellongitudinal slots 40 in which a pair of endless flexible belts 42operate. The belts 42 are toothed belts which are drawn around sprockets44 carried on a common shaft 46 at the input or upstream end of themagazine 12. The shaft 46 is supported for rotation by a pair ofbearings 48 secured to the frame of the machine. The opposite orupstream ends of the belts are similarly drawn around sprockets 50(FIGS. 1 and 2). The sprockets 44 and 50 locate the upper runs of thebelts 42 slightly above the conveyor surface provided by the inclinedfloor panel 36.

As best shown in FIG. 6, each belt 42 is provided with a plurality ofteeth 42a which project from both surfaces of the belt. The teeth 42aare equally spaced and extend transversely across the entire width ofthe belt. Between each pair of teeth 42a, a groove 42b is formed to alsoextend transversely across the width of the belt. The teeth 42a whichproject from the inside surfaces of the belt are engaged by thesprockets 44 and 50 so that the belts are driven by the sprockets. Thegrooves 42b are wide enough to accommodate the edges of the envelope E.

A third toothed belt 52 is supported to travel generally along the topedge of the inclined side panel 38. Belt 52 is constructed in the samemanner as belts 42 and is provided with teeth and grooves identical toteeth 42a and grooves 42b. The upstream end of belt 52 is drawn around asprocket 54 which is carried on the top end of a shaft 56. The shaft 56is inclined slightly from vertical and supported for rotation by a pairof bearings 58 secured to the frame of the machine. The opposite ordownstream end of belt 52 is similarly drawn around another sprocket 60(see FIG. 2). The sprockets 54 and 60 locate the forward run of belt 52such that it projects slightly beyond the side panel 38.

The belts 42 and 52 are driven by a multiple speed electric motor 62which is secured to a mounting panel 64 on the frame of the machine. Themotor 62 has an output shaft 66 which is coupled end to end with anothershaft 68 by a coupling 70. The opposite end of shaft 68 is received by abearing 72 mounted on the frame of the machine. Shaft 68 carries twopulleys 74. Additional pulleys 76 and 78 are mounted on shafts 46 and56, respectively. A drive belt 80 is drawn around pulley 76 and istwisted and passed around both pulleys 74 before being twisted again andpassed around pulley 78. Consequently, the operation of motor 62 drivesbelts 42 and 52 at the same speed and in the same direction from theupstream end of magazine 12 toward the downstream end.

The downstream or discharge ends of the belts 42 terminate at ahorizontal panel 82 which receives the lower edges of the envelopes thatare fed to the pickoff station 14 by the feeding mechanism. A grooveroller 84 and a smaller smooth roller 86 project upwardly above panel82. Another grooved roller 88 is located at the end of the side panel 38and receives the side edges of the envelopes that are conveyed to theend of the side panel. Roller 88 is elevated with respect to the otherrollers 84 and 86.

The envelope pickoff device located at the pickoff station 14 includes apair of vacuum belts 90 each drawn around a pair of front rollers 92 anda single back roller 94. The front rollers 92 locate the front runs ofthe vacuum belts 90 perpendicular to the direction of movement of theenvelopes along the magazine section 12 of the machine. A triangularplate 96 is located above the rollers. As described in theaforementioned Akers U.S. Pat. No. 4,275,875, the vacuum belts 90 haveopenings 98 (see FIG. 3) which communicate with a vacuum source in orderto draw the flat front faces of the envelopes against the front surfacesof the vacuum belts. The grooved rollers 84 and 88 are driven by anappropriate drive system (not shown) in order to feed the envelopes tothe vacuum belts 90. A tapered guide plate 100 helps to guide eachenvelope as it approaches the vacuum belts.

A switch 102 is located between the two vacuum belts 90, as best shownin FIG. 3. The switch 102 normally projects beyond the vacuum belts 90such that it is depressed when an envelope is located at the pickoffstation 14 (shown in FIG. 1) and drawn by vacuum against the belts 90.The switch 102 thus senses the presence or absence of an envelope at thepickoff station since it is depressed when there is an envelope presentand is released when there is not an envelope present at the pickoffstation.

As shown in FIG. 3, the vacuum belts 90 are driven by the drive roller94 which is shown in FIG. 2 as mounted on a vertical shaft 104. Thelower end of shaft 104 carries a sprocket 106 which receives a drivechain 108. The chain 108 is driven at a suitable speed to move belts 90in the proper direction to convey the picked off envelopes one at a timeinto the guide way 20. Guide rollers 110 oppose the vacuum belts 90 toassist in guiding the individual envelopes into the guide way.

As shown in FIG. 2, a pair of belts 112 oppose one another on oppositesides of the guide way 20 in order to convey the individual envelopesfrom the pickoff station 14 to the first set of deflector gates 22 inthe storage section 18 of the machine. Once the envelopes reach thestorage section, they are conveyed in the manner shown in theaforementioned Akers U.S. Pat. No. 4,275,875 or in any other suitablemanner. The belts 112 are drawn around rollers 114, and the rollers aredriven at the proper speed by a suitable drive system (not shown).

The operation and speed of the electric drive motor 62 are controlled bythe electronic control system shown schematically in FIGS. 7 and 8.Referring first to FIG. 7, the control system includes a 555 timercircuit 116 having an output line 118 to which 6.6 millisecond squarewave clock pulses are applied by the timer. Line 118 connects with anAND gate 120 and with the clock input to a flip-flop circuit 122 whichfunctions as a divide by two counter. The Q output line 124 of flip-flop122 receives 13.2 millisecond square wave clock pulses which are appliedto another AND gate 126.

The switch 102 which senses the presence or absence of an envelope atthe pickoff station 14 has an output line 128 which connects with avoltage source through a pull up resistor 130. The switch output line128 is in a low condition when switch 102 is depressed by an envelope atthe pickoff station. When there is no envelope at the pickoff station,the switch 102 is released and line 128 is pulled to a high statethrough the pull up resistor 130. The output line 128 of the switchconnects directly with AND gate 126 and through inverter 132 with theother AND gate 120.

An up/down counter 136 has its "down" input connected with the output ofgate 120 through an inverter 138. The output from the other AND gate 126is connected through an inverter 140 with the "up" input of counter 136.An initial count state of seven (binary 0111) is preset on the counter136. The B and C or borrow and carry outputs of the counter 136 areconnected with respective lines 136a and 136b forming the inputs to anAND gate 142 having its output line connected with the clock input of aflip-flop 144. The Q output line of the flip-flop 144 is connected withan inverter 146 having its output side connected with the load terminalof the up/down counter 136. When a low signal is delivered to the loadinput of counter 136, the preset count state of seven is loaded into thecounter.

The B output line 136a of the up/down counter 136 connects via line 148with the input side of a tri-state circuit 150. The output side ofcircuit 150 is connected with the down input of another up/down counter152. Voltage is applied to the output line of circuit 150 through apull-up resistor 154. Line 156 connects the C output line 136b ofcounter 136 with the input side of another tri-state circuit 158. Theoutput side of circuit 158 is connected with the up input of counter152. Voltage is applied to the output line of circuit 158 through apull-up resistor 160. Counter 152 has an initial or preset count stateof zero.

The binary coded QA and QB outputs of counter 152 are connected withrespective output lines 162 and 164 which connect with the A0 and A1address terminals of a data selector 166. The QC and QD outputs ofcounter 152 are not used. The third address line A2 of data selector 166is connected with ground.

The data selector 166 has an S1 input line 168, an S2 input line 170, anS3 input line 172, and an S4 input line 174. A different voltage isapplied to each of these lines. Preferably, the voltages that areapplied to the input lines of the data selector are derived from themotor controller (not shown) for the electric drive motor 62. By using asuitable voltage divider in association with the motor controller, aselected minimum voltage can be applied to the S1 input line 168, and aselected maximum voltage can be applied to the S4 input line 174.Intermediate voltages can be applied to the S2 and S3 lines 170 and 172.It is preferred that the voltage increments between each successive linebe the same so that the drive motor speed change is effected in equalincrements. The data selector 166 has a D output line 176 which leads tothe motor controller and which applies to the motor controller thevoltage the selected input line, which depends upon the state of theaddress lines 162 and 164. The drive motor 62 increases in speedproportionally to the increasing voltage which is applied to the outputline 176.

Line 162 connects via line 178 with an AND gate 180 and also with aninverter 182. The output side of inverter 182 connects with another ANDgate 184. Line 186 connects the QB output line 164 with gate 180 andwith an inverter 188 having its output side connected with the secondinput of the other AND gate 184.

Gate 180 has an output line 190 which controls tri-state circuit 158.The tri-state device is enabled when line 190 is a low state and isdisabled when line 190 is in a high state. Similarly, the output line192 of gate 184 is used to control the other tri-state circuit 150.Circuit 150 is enabled when line 192 is in a low state and is disabledwhen line 192 is in a high state.

Extending from line 178 is a conductor 194 which, as shown in FIG. 8,connects with an AND gate 196 and also with an inverter 198. The outputside of the inverter 198 is connected to one input of another AND gate200. Another conductor 202 connects with line 186 and leads to aninverter 204 and also to the other input of gate 200. The output frominverter 204 is the second input to gate 196.

With continued reference to FIG. 8, a visual display of the speed atwhich the drive motor 62 is operating is provided by four light emittingdiodes. The first LED 206 connects on its anode side with the outputline 192 from gate 184. The second and third LED's 208 and 210 connectwith the output sides of the respective AND gates 196 and 200. Thefourth LED 212 connects with line 190. The cathode sides of the LEDS areconnected with ground through suitable resistors.

As previously described, the output line 118 of timer 116 receives 6.6millisecond clock pulses. A counter 214 (FIG. 8) has its clock inputconnected with line 118 to receive the clock pulses emitted by the timer116. The QA and QB output lines of counter 214 are not used. The QC andQD output lines are connected to the inputs of an AND gate 216. Theoutput signal from gate 216 is applied to the clock input of a flip-flop218 having its Q output line connected with an inverter 220. Theinverter has an output line 222 which, as shown in FIG. 7, is used toenable and disable the data selector 166. When line 222 is in a highstate, the data selector is disabled by the application of voltagethrough a resistor 224. The data selector is enabled when line 222 is ina low state.

The clear lines of counter 214 and flip-flop 218 are controlled by theoutput line 134 from inverter 132. The counter 214 and the flip-flop 218are cleared when line 134 is placed in a high state due to depression ofthe switch 102 by an envelope located at the pickoff station 14 of themail sorting machine.

In operation of the machine, the envelopes E that are to be sorted areloaded in a stack onto the floor panel 36 of the magazine section 12.The envelopes E are arranged side-to-side with each envelope occupying avertical plane. The long lower edge of each envelope rests on theconveyor surface provided by the floor panel 36 and the belt 42. Oneside edge of each envelope rests against the side panel 38 and theelevated belt 52. The front faces of the envelopes face in a downstreamdirection.

The grooves 42b of the belts 42 are each wide enough to receive thelower edge of one envelope. Similarly, the side edge of each envelope isreceived in the groove formed between adjacent teeth of the elevatedbelt 52. The grooves in the belts are aligned so that each envelope isoriented perpendicular to the direction it is moved by the envelopefeeding mechanism.

The drive motor 62 operates to drive belts 42 and 52 at the same speedso that the envelope supply is conveyed toward the pickoff station 14.Because the belts move at the same speed, the grooves which receive eachenvelope remain in alignment so that the envelopes are not skewed orotherwise disoriented as they travel along the magazine section 12 ofthe machine. The elevated belt 52 helps to convey the envelopes andassures that each envelope remains in an upright posture at all times.The drive belts define a straight conveyor path between the input anddischarge ends of the magazine 12.

When the leading envelope in the envelope supply reaches the pickoffstation 14, it is discharged from belts 42 and 52 onto the panel 82 andthe rollers 84 and 86. The side edge of each envelope is received in thegrooves of the elevated roller 88. The grooved rollers 84 and 88 aredriven to advance the envelope toward the vacuum belts 90 which pick theenvelopes off one at a time from the envelope supply. The vacuum whichis applied through the vacuum openings 98 in the vacuum belts draws theleading envelope firmly against the belts so that the envelopes aredelivered one at a time into the guide channel 20 along which they areconveyed by belts 112. The code imprinted on the face of the envelope isread at the read station 16, and the deflector gate 22 corresponding tothe code is deflected to divert the envelope into the appropriatestorage bin or other storage area in the storage section 18 of themachine.

The speed at which the drive motor 62 drives belts 42 and 52 isdetermined by the binary coded signal applied to lines 162 and 164. Forexample, if both lines are in a low state, both the A0 and A1 addresslines are in a low state and the data selector 166 selects the voltageon the S1 line 168. This minimum voltage level is applied to the Doutput line 176 and causes the motor 62 to operate at its minimum speed.If line 162 is high and line 164 is low, the binary 01 address isselected and output line 176 receives the voltage on the S2 input line170 so that the motor runs at the next lowest speed. A high state online 164 and a low state on line 162 results in application of thevoltage on the S3 line 172 to the output line 176, thereby operating themotor at the next to the highest speed. Finally, if both lines 162 and164 are high, the binary 11 address is selected and the maximum voltageon the S4 input line 174 is applied to line 176 to operate the drivemotor at its maximum speed.

When counter 152 is in the zero count state, both lines 162 and 164 arelow and gate 184 then applies a high signal on its output line 192. Thishigh signal disables the tri-state circuit 150 and prevents counter 152from being decremented. Similarly, when counter 152 reaches its maximumcount state (binary 11), both lines 162 and 164 are high, and gate 180applies a high signal on its output line 190. This disables tri-statedevice 158 and prevents counter 152 from being incremented. In thismanner, the logic gates 180 and 184 and tri-state circuits 150 and 158prevent counter 152 from being decremented below its minimum count stateof zero or incremented above its maximum count state of binary 11.

The LED display provides a visual display of the speed at which themotor operates. When lines 162 and 164 are both low indicating the lowspeed of the motor, line 192 is in a high state to energize the firstLED 206 which corresponds to the low motor speed. The other LEDs are offwhen line 162 is high and line 164 is low, line 194 is high and line 202is low, thereby activating gate 196 and energizing LED 208 to indicatethat the motor is operating at its second lowest speed. When line 162 islow and line 164 is high, line 202 is high and line 194 is low so thatgate 200 is activated to energize LED 210, indicating that the motor isoperating at its second highest speed. Finally, when lines 162 and 164are both high, line 190 energizes LED 212 to indicate that the motor isoperating at its highest speed level. The logic circuitry prevents morethan one LED to be energized at any one time.

The operation and speed of the drive motor 62 are controlled by thecontrol circuitry shown in FIGS. 7 and 8. When an envelope is present atthe pickoff station 148, it depresses switch 102 and thereby places line128 in a low state. Since one input to gate 126 is low, the clock pulsesapplied to line 124 have no effect and a high signal is applied to theup input of the up/down counter 136.

However, line 134 is in a high state and the output of gate 120 cycleshigh and low in response to the 6.6 millisecond clock pulses present online 118. Each clock pulse which reaches the down input of counter 136decrements the count state from the preset count state of seven. Ifswitch 102 remains depressed long enough for the count to be decrementedto zero (46.2 milliseconds), the B or borrow output line 136a of counter136 is activated and a signal is applied to the down input of counter152 through line 148 and tri-state circuit 150. The down signaldecrements the count state of counter 152 and changes the binary codedsignal applied to the QA and QB output lines 162 and 164.

Thus, each time the switch 102 remains depressed for 46.2 milliseconds,the count state of counter 136 is reduced to zero and the count state ofcounter 152 is decremented. This in turn decrements the address signalapplied to data selector 166 and causes the drive motor 62 to slow downto the next lower speed so that the feeding mechanism delivers theenvelopes to the pickoff station 14 at a slower rate. So long as switch102 remains depressed, the circuitry continues to decrement the motorspeed until the minimum speed setting is reached, at which timetri-state circuit 150 is disabled to prevent counter 152 from beingfurther decremented.

When there is not an envelope present at the pickoff station 14, switch102 is released and line 128 is pulled to the high state throughresistor 130. Gate 120 then receives a low input through inverter 132 sothat the down input of counter 136 is not affected by the clock pulseson line 118. However, gate 126 receives a high signal on one input, andits other input is cycled by the 13.2 millisecond clock pulses that arepresent on line 124. Each clock pulse which reaches the up input ofcounter 136 increments the count state. When the maximum count state of16 (binary 1111) is reached, the C output line 136b of counter 136 isactivated to signal the up input of counter 152 through line 156 andtri-state circuit 158. Counter 152 is thus incremented to increment thebinary coded address signal which is applied to the data selector 166.The drive motor 62 is then incremented by one discrete speed level. Solong as the switch 102 is not depressed, the drive motor speed continuesto increment until the highest speed level is reached, at which timetri-state circuit 158 is disabled to prevent counter 152 from beingfurther incremented.

Counter 136 is reset to its initial count state of seven each timeeither its B output line 136a or C output line 136 is activated. Aspreviously indicated, a high signal is applied to either the up or downinput to counter 136 at all times, and either line 136a or 136b is highas a consequence. When counter 136 is decremented to 0 or incremented tosixteen, the other line 136a or 136b goes high to activate gate 142. Theclock signal to flip flop 144 causes the Q output line of the flip flopto go high, and inverter 146 applies a low signal to the load terminalof counter 136. This causes the counter to revert to its present countstate.

In this manner, the speed at which envelopes are fed to the pickoffstation 14 is controlled in accordance with the state of switch 102. Ifthe switch is depressed long enough to indicate that the envelopes arebunched together too tightly, the drive motor speeed is decremented bydiscrete levels and at regular intervals. Conversely, if switch 102remains in the released condition long enough to indicate that theenvelopes are not being fed to the pickoff station fast enough, thedrive motor speed is incremented at regular intervals by discrete speedlevels. It should be noted that if the switch 102 is depressed andreleased in a pattern indicating that the envelopes are arranged neithertoo tightly nor too loosely, the count state of the up/down counter 136will remain between zero and sixteen, and the speed setting of the motorwill not change.

It is an important feature of the invention that the motor speed isdecremented at more frequent intervals than it is incremented because itis more important to prevent the envelopes from bunching together tootightly than it is to cure an unduly loose condition of the envelopes.The down input to counter 136 is controlled by the 6.6 millisecond clockpulses that are applied to line 118, while the up input to the counteris controlled by the 13.2 millisecond pulses that are applied to line124. In addition, counter 136 has a preset count state of seven which iscloser to the minimum count state of zero than it is to the maximumcount state of sixteen. As a consequence, the drive motor is decrementedby one speed level each time switch 102 remains depressed for 46.2milliseconds. However, switch 102 must be released for 118.8milliseconds before the drive motor is incremented to its next higherspeed setting.

The control circuitry also acts to shut down the drive motor in theevent that its speed is decremented by one speed setting and theenvelopes still remain bunched too tightly together. When switch 102 isdepressed, the high signal on line 134 is applied to the clear terminalsof counter 214 and flip-flop 218. Counter 214 then begins to count the6.6 millisecond clock pulses which are applied on line 118 to its clockinput. When the count state of counter 214 reaches twelve (binary 1100),indicating that switch 102 has been depressed continuously for 79.2milliseconds, the QC and QD output lines of counter 214 are both placedin a high condition to activate gate 216. The gate then applies a signalto the clock input of flip-flop 218, and line 222 receives a signalthrough inverter 220 to disable the data selector 166. In the disabledcondition of the data selector, the output line 176 is deactivated todeactivate the drive motor 62 of the envelope feeding mechanism.

The drive motor is thus disabled only if switch 102 remains depressedcontinuously for 79.2 milliseconds. Since the drive motor is decrementedby one speed setting each time switch 102 remains depressed for 46.2milliseconds, the motor will be deactivated only if the tightly bunchedcondition of the envelopes remains for another 33.4 milliseconds afterthe motor speed has been decremented by one speed level. This gives thespeed control system sufficient time to relieve the tightly bunchedcondition of the envelopes, and if it is not able to do so, the motor isdeactivated. If switch 102 is released before 79.6 milliseconds haveelapsed, counter 214 is cleared along with flip-flop 218 so that the79.2 millisecond shut off time interval is again initiated.

It is important to recognize that the speed control circuitry isindependent of the motor shut off circuitry. Consequently, the speedsetting of the drive motor continues to be decremented even while thedrive motor is shut off. Thus, if the drive motor is off for arelatively long time, indicating that the envelopes are very tightlybunched, the speed setting of the drive motor will be decremented to itslowest level since the counters 136 and 152 continue to operate whetheror not the drive motor is activated. When switch 102 is finallyreleased, the drive motor 62 is activated and comes on at its lowestspeed setting to prevent the envelopes from being tightly bunchedagainst the pickoff station 14. Conversely, if the motor remains off foronly a short time period, indicating that the envelopes are not undulybunched together, the motor will come back on at approximately the samespeed as it was operating when it was deactivated, or at the next lowerspeed level.

It is thus apparent that the present invention provides an improvedfeeding mechanism for feeding the envelope supply to the pickoff station14 of the mail sorting machine. The drive belts 42 which underlie theenvelope supply, along with the elevated belt 52 which controls the sideedges of the envelopes, are able to maintain the envelopes in the properupright posture and orientation as they approach the vacuum belts 90.Consequently, the feeding mechanism is less prone to double envelopepicking and other mispicking problems than some of the other feedingmechanisms that have been proposed in the past.

The circuitry which controls the speed and operation of the drive motor62 automatically maintains the envelopes in a condition in which theyare bunched together neither too tightly nor too loosely. The automaticmanner in which the speed control and motor shutoff systems operateeliminates human error and does not require the constant attention of ahuman operator to function properly. The speed settings at which motor62 drives the feeder belts 42 and 52 are separated by discrete levelsand may differ from the four speed settings disclosed herein.

From the foregoing, it will be seen that this invention is one welladapted to attain all the ends and objects hereinabove set forthtogether with other advantages which are obvious and which are inherentto the structure.

It will be understood that certain features and subcombinations are ofutility and may be employed without reference to other features andsubcombinations. This is contemplated by and is within the scope of theclaims.

Since many possible embodiments may be made of the invention withoutdeparting from the scope thereof, it is to be understood that all matterherein set forth or shown in the accompanying drawings is to beinterpreted as illustrative and not in a limiting sense.

Having thus described the invention, we claim:
 1. In a mail sortingmachine having a magazine section for receiving a supply of envelopes tobe sorted, pickoff means for picking off the envelopes one at a timefrom the envelope supply, multiple speed feeding means for feeding theenvelope supply in said magazine section to said pickoff means, andmeans for sorting and depositing the envelopes in a storage area of themachine, the improvement comprising:means for sensing the presence orabsence of an envelope at a pickoff station adjacent the pickoff means;means for automatically decreasing the speed of the feeding means whenan envelope is present at said pickoff station for a first predeterminedtime period selected as being indicative of undue bunching of theenvelopes in the magazine section of the machine; and means forautomatically increasing the speed of the feeding means when an envelopeis absent from said pickoff station for a second predetermined timeperiod selected as being indicative of undue looseness of the envelopesin the magazine section of the machine.
 2. The invention of claim 1,wherein said second time period is greater than said first time period.3. The invention of claim 1, including means for deactivating thefeeding means to stop the movement of the envelope supply in themagazine section of the machine when an envelope is present at saidpickoff station for a third predetermined time period.
 4. The inventionof claim 3, wherein said third time period is greater than said firsttime period.
 5. Envelope feeding apparatus for a mail sorting machinehaving a magazine section for receiving a supply of envelopes to besorted, means for picking off the envelopes one at a time from theenvelope supply at a pickoff station, and means for sorting anddepositing the envelopes in a storage area of the machine, said envelopefeeding apparatus comprising:feeding means for feeding the envelopesupply in the magazine section to the pickoff station; multiple speeddrive means for driving said feeding means, said drive means havingactive and inactive states and a plurality of discrete speed settingsfor driving said feeding means at a plurality of discrete speeds whensaid drive means is in the active state; switch means engageable byenvelopes at the pickoff station, said switch means having a firstcondition when an envelope is present at the pickoff station and asecond condition when an envelope is not present at the pickoff station;means for decrementing said drive means from one speed setting to thenext lower speed setting each time said switch means has been in thefirst condition for a first predetermined time period; and means forincrementing said drive means from one speed setting to the next higherspeed setting each time said switch means has been in the secondcondition for a second predetermined time period.
 6. The invention ofclaim 5, wherein said first time period is less than said second timeperiod.
 7. The invention of claim 5, including means for effecting theinactive state of said drive means each time said switch means has beenin the first condition for a third predetermined time period greaterthan said first time period.
 8. The invention of claim 7, wherein saiddecrementing means and said incrementing means are operable to changethe speed setting of said drive means in both the active and inactivestates of said drive means.
 9. The invention of claim 5, wherein saiddiscrete speed settings include a minimum speed setting and a maximumspeed setting, and including:means for disabling said decrementing meanswhen said drive means is in the minimum speed setting; and means fordisabling said incrementing means when said drive means is in themaximum speed setting.
 10. The invention of claim 5, including means fordisplaying the speed setting of said drive means.
 11. In a mail sortingmachine having a magazine section for receiving a supply of envelopes tobe sorted, pickoff means for picking off the envelopes one at a timefrom the envelope supply at a pickoff station, feeding means for feedingthe envelope supply in the magazine section to the pickoff station, andmeans for sorting and depositing the envelopes in a storage area of themachine, the improvement comprising:drive means for driving said feedingmeans, said drive means having active and inactive states and aplurality of discrete speed settings for driving said feeding means at aplurality of discrete speeds in the active condition of said drivemeans; a switch at the pickoff station engaged by an envelope present atthe pickoff station to effect a first condition of the switch, saidswitch having a second condition when an envelope is not present at thepickoff station to engage the switch; counter means operable to countdown toward a minimum count state when said switch is in the firstcondition and to count up toward a maximum count state when said switchis in the second condition; means for decrementing said drive means tothe next lower speed setting each time said minimum count state isreached; means for incrementing said drive means to the next higherspeed setting each time said maximum count state is reached; means forresetting said counter means to an initial count state between theminimum and maximum count states each time said drive means isincremented or decremented; and means independent of said counter meansfor effecting the inactive state of said drive means when said switchhas been continously in the first condition for a predetermined timeperiod.
 12. The improvement of claim 11, wherein said counter meanscounts down toward the minimum count state at a faster rate than itcounts up toward the maximum count state.
 13. The improvement of claim11, wherein said discrete speed settings of said drive means includeminimum and maximum speed settings and including:means for disablingsaid decrementing means when said drive means is in the minimum speedsetting; and means for disabling said incrementing means when said drivemeans is in the maximum speed setting.
 14. The improvement of claim 11,including means for displaying the speed setting of said drive means.15. An envelope feeding mechanism for feeding envelopes to an envelopepickoff device in a mail sorting machine, said mechanism comprising:aconveyor surface defining a generally straight conveyor path having aninput end and a discharge end located adjacent the pickoff device, saidconveyor surface being inclined from side to side and being adapted toreceive a supply of envelopes with the envelopes arranged side to sideand each envelope having a lower edge thereof on the conveyor surfaceand oriented transversely to said conveyor path; first and secondtoothed belts supported on the machine for movement generally along saidconveyor path from the input end to the discharge end thereof to deliverthe envelopes in the envelope supply to the pickoff device one at atime, each belt having a plurality of teeth between which grooves arepresented for receiving the lower edges of the envelopes; a side panelprojecting upwardly from a low side of said conveyor surface, said sidepanel being inclined from vertical and oriented substantiallyperpendicular to said conveyor surface to receive side edges of theenvelopes that are being conveyed on the conveyor surface; a thirdtoothed belt supported on the machine for movement generally along saidside panel at an elevated position relative to said first and secondbelts, said third belt having a plurality of teeth between which groovesare presented for receiving the side edges of the envelopes to maintainthe envelopes generally upright and to assist in conveying the envelopesalong said conveyor path; and drive means for driving all of said beltsat substantially the same speed, whereby the envelopes are maintainedgenerally upright with the lower edges thereof remaining transverse tothe conveyor path as the envelopes travel along said path.
 16. Theinvention of claim 15, including:a multiple speed drive motor coupledwith said belts to provide said drive means, said motor having activeand inactive states and a plurality of discrete speed settings fordriving said belts at a plurality of different speeds in the activestate of the motor; means for sensing the presence of absence of anenvelope at a pickoff device, said sensing means having a firstcondition when an envelope is present at the pickoff station and asecond condition when an envelope is not present at the pickoff station;means for decrementing said motor to the next lower speed settingthereof when said sensing means is in the first condition for a firstpredetermined time period; and means for incrementing said motor to thenext higher speed setting thereof when said sensing means is in thesecond condition for a second predetermined time period.
 17. Theinvention of claim 16, including means for effecting the inactive stateof said motor when said sensing means is in the first condition for athird predetermined time period greater than said first time period. 18.The invention of claim 16, wherein said second time period is greaterthan said first period.
 19. The invention of claim 16, wherein saiddecrementing means and said incrementing means are operable to changethe speed setting of said motor in both the active and inactive statesof the motor.
 20. The invention of claim 16, wherein said discrete speedsettings of the motor include a minimum speed setting and a maximumspeed setting and including:means for disabling said decrementing meanswhen said motor is in the minimum speed setting; and means for disablingsaid incrementing means when said motor is in the maximum speed setting.21. A method of feeding envelopes to an envelope pickoff station in amail sorting machine, said method comprising the steps of:arranging aplurality of envelopes side to side on a movable conveyor with eachenvelope occupying a substantially vertical plane; driving the conveyortoward the pickoff station to deliver the envelopes thereof; sensingwhether or not an envelope is present at the pickoff station; decreasingthe speed at which the conveyor is driven when an envelope is present atthe pickoff station for a first predetermined time period selected asbeing indicative of undue bunching of the envelopes on the conveyor; andincreasing the speed at which the conveyor is driven when an envelope isnot present at the pickoff station for a second predetermined timeperiod selected as being indicative of undue looseness of the envelopeson the conveyor.
 22. The method of claim 21, wherein said second timeperiod is greater than said first time period.
 23. The method of claim21, including the step of stopping the conveyor when an envelope ispresent at the pickoff station for a third predetermined time periodgreater than said first period.
 24. The method of claim 21, wherein theconveyor has a plurality of discrete speeds at which it is driven andthe speed of the conveyor is decreased and increased by discrete levels.25. The method of claim 24, wherein the discrete speeds of the conveyorinclude a minimum speed and a maximum speed, said method including thesteps of:preventing additional decrease in the speed of the conveyorwhen the conveyor is being driven at said minimum speed; and preventingadditional increase in the speed of the conveyor when the conveyor isbeing driven at said maximum speed.
 26. The method of claim 24,wherein:said decreasing step includes counting down toward a minimumcount state when an envelope is present at the pickoff station anddecrementing the speed of the conveyor to the next lower speed when theminimum count state is reached; and said increasing step includescounting up toward a maximum count sate when an envelope is not presentat the pickoff station and incrementing the speed of the conveyor to thenext higher speed when the maximum count state is reached.
 27. Themethod of claim 26, including the step of stopping the conveyor when anenvelope is present at the pickoff station for a third predeterminedtime period greater than said first time period, said stopping stepbeing carried out independently of said steps of counting up andcounting down.